Reversible cycle heat pump



June 28, 1949. G. E. cLANcY 2,474,304

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REVERSIBLE CYCLE HEAT PUMP Filed Jan. 28, 194e 5 Shee'ts-Sheqt 5 Jnr/enaz'" EziJbrJ-" E.. Clancy MMM@ REVERSIBLE CYCLE HEAT PUMP Gilbert E. Clancy, Los Angeles, Calif., signor to Buyer-Hanson, Log Angeles, Calin, a oopartnership Application Jennery 2s, 1m. serai No. 043,941

-heat from a cool surrounding medium, such as outdoor air, to the space to be heated. When air conditioning requires provision for both cooling and heating, the same heat exchanging plant can be `designed to perform both functions economically. This has many advantages, such as simplicity of maintenance, uniformity of load factor on a single power service, and the avoidance of long idle periods for part of the equipment.

The present invention is concerned with improvements in such dual purpose systems to make them less costly and more eillcient; with improved arrangements for switching such systems from one function to the other; with a newftype of heat exchanging unit which can be designed to give optimum effectiveness whichever function is being performed; and with an electrical control 'system which provides completely automatic defrosting of the evaporator unit in the outside air stream. Before describing my invention more fully, I shall outline the operation of the reversible cycle system and describe briefly` the difilculties usually encountered in-switching it from one function to the other.

A power driven compressor delivers refrigerant .vapor at relatively high temperature and pressure to a condenser. This is aheat transfer unit in which heat is given up by the refrigerant to an air stream (use ofl other heat carriers'will be considered later), condensing the refrigerant vapor to the liquid state. The temperature vof the condenser lis essentially determined by the boiling point of the refrigerant at the relatively high pressure maintained by the compressor. The liquid refrigerant then passes through an expansion valve, by which its pressure and temperature are reduced to relatively low values in an essentially isodynamic (constant total heat) expansion. The refrigerant liquid enters a second heat' exchange unit, the evaporator, in which heat is taken up by the refrigerant from a second ai'r stream, evaporating the refrigerant liquid to the ,vapor state again. The temperature of the evaporator is essentially determined by the boiling point of the lrefrigerant at its reduced pressure, and is therefore lower than the temperature of the condenser. The pressure in the evaporator air stream at a higher temperature.

is maintained at its relatively low value bythe compressor. which draws off the refrigerant vapor as it is formed. compresses it to the initial relatively high pressure and temperature', and returns it to the condenser, repeating the cycle. The net effect of the complete c'ycle is to remove heat from the evaporator air stream at a lower temperature and to deliver heat to the condenser To apply this system to air conditioning it'ls only necessary to circulate air to be 'conditioned through the condenser or the evaporator, according as it needs to be heated or cooled; and in either case. to circulate outside air through the other unit.

The energy needed to pump heat from the lower to the higher temperature is provided in the form of mechanical energy to drive the compresser. Ideally, all of this energy reappears in the form of heat delivered to the condenser air stream. Therefore the total amount of heat delivered by the heat pump at the higher temperaturegis greater than the heat taken in at the lower temperature, the difference corresponding approximately to the energy expended in the compressor. Moreover, these three quantities, the heat delivered to one air stream, the heat taken in from the other air stream, and the energy expended, are proportional, respectively, (for an ideal system) to the absolute temperature ofthe condenser, the absolute temperature of the evaporator, andthe difference between these two absolute temperatures. For example, if the absolute condenser temperature is 318 Kelvin and the absolute evaporator temvtheoretical eillciency of the system, Vconsidered as a means of cooling the evaporator air stream. Thus the amount of heat usefully transferred in heating or cooling is, in this instance, roughly five times the energy expended in the compressor. In other words, under the assumed conditions, a building can be heated five times as effectively by a given amount of electrical energy, say, if this is used to pump heat in from the colder outside air than if lt is converted directly into heat.

' Irwin be seen at blast e611 so that it wm' am effectively both as (and other similar temperaturedrops in the system) is to be kept to a minimum, each heat exchange unit must be carefully designed for'the particular function it is to perform. The design should take into account not onlywhether a given coil is to act as evaporator or condenser, but also whether it is to be located -in the conditioned airstream or in the outside air stream. This is because it is economical to .use large quantities of air in the outsideair stream, thus reducing the necessary' temperature difference between air and refrigerant; but the amount of ain-which may be economically circulated in the conditioned air stream is limited Iby power losses in the relatively long air ducts, and by other con- (y siderations. These facts are of particular importance in the design of a system intended to be switched back and forth between heating and cooling the conditioned space.

One manner of switching, which I shall call system A, is to use a condenser coil in one air duct and an evaporator coil in another air duct,

and to switch the air streams between the two' ducts. For heating, the' conditioned air stream is passed through the condenser duct and the outside air stream through the evaporator duct.

For cooling, the conditioned air stream is switched.

by a system of dampers to the evaporator duct, and the outside' air stream is automatically switched at the same time to the condenser duct. An advantage of this air switching method of. cha'nging function is that the refrigerant cycle is always the same, the evaporator and the condenser always serving the same purpose in the same way. However, the air ducts and switching equipment occupy a. considerable amount of, space. A more important disadvantage arises from the verydiil'erent quantities of air that must be handled in theoutside air'y stream and in the conditioned air stream to give a practical effective efficiency. 'I'his necessitates the design of both blast coils with large enough face area to pass the larger quantity of air, increasing the bulk and first cost of the equipment and making it difficult to obtain good balance. Several variations of this system have been used, but they show the same general characteristics and need not be described here.4

The disadvantages of air switching can be avoided by the use of refrigerant switching systems. mand attention, and will 'be denoted as systems B and C. In both of these the conditioned air is always circulated through one duct and the outside air through another. In system B there is one refrigerant coil in each duct, which acts as condenser or evaporator according to whether that air stream is to be heated or cooled. The

refrigerant circuit in Athis system is relatively complex, because of the number of automatic valves which are required to control the flow.

Four three-way valves or their equivalent are needed. In addition, it is difficult to design a Two forms of refrigerant switching decondenser and as evaporator.

In the second refrigerant switching system C, two blast coils are provided in each of the air ducts, one serving only as condenser and the other only as evaporator. Only two three-way valves (or their equivalent) are required with this arrangement. Bince each of the four blast coils is used for only one function, it can be designed to'perform that function with satisfactory emciency. The chief disadvantages of this system are the increased air friction due to the duplicationof blast coils in each air stream.- and the increased weight, bulk and expense ofthe 'additional coils. A

The present invention makes possible a reversible cycle air conditioning system which in large measure combines the advantages of the two last described systems but avoids their characteristic disadvantages. In each air stream a single blast coil unit is used, as in system B, but this is constructed with two separate primary or refrigerant tube circuits, one designed to perform eillcientiy the function of condenser and the other designed expressly as an evaporator. The secondary surface of each blast coil, at which heat exchange with the air takes place. is common to both of the primary tube circuits. This secondary'surface may consist of conventional flat fins, brought into heat conducting relation with the tubing of the two refrigerant circuits by any suitabletechnique. Eachy iin is common to some, but not necessarily 'to all, of the tubes of both circuits. Switching is performed by switching the refrigerant.

There are certain other `i'eatu'res of the invention associated with the coil units, and a controlling system, which will be explained.

VThe various features of the new system are illustrated in the accompanying gures, of which:

Figs. 1 and 2 illustrate diagrammatically a preferred embodiment of the invention, Fig. 1 showing the system as use'd'for heating the conditioned space, and Fig. 2 for cooling;

Figs. 3, 3a and 3b are respectively side elevation, end elevation and plan of a typical `blast coil designed according to my invention for the condi'- tioned air stream and having separate tube circuits for condenser and evaporator;

Fig. 3c is a section taken at 3c-3c of Fig. 3b;

Figs. 4, 4a, and 4b are respectively side elevation, end elevation and plan of a similar blast coil designed according to-my invention for use in the outside air stream;

Fig. 4c is a section taken at Ic-Ic of Fig. 411;.

Fig. 5 is a section of an injector nozzle associated with the coil units, taken at 5-5 in Fig. 3 or Fig. 4;

Fig. 6 shows in partial section the special switching valve, indicated at 20 in Figs. 1 and 2;

Fig. 7 is a diagram of the electrical control circuit for the entire system.

Referring now to Figs. 1 and 2, the action of my system nis 'as follows. Return air from the conditioned s enters e A at Il and is recirculated to e space by the blower j! after passing through the conditioning blast coil unit, indicated at Il. Similarly, outside air enters passage B at I2, passes through the outside air blast coil unit Il and is drawn of! and rejected to the outside by the blower 3L Each blast coil unit is seen to contain two tube circuits, both related to the common secondary surface, such as the fins represented schematically at I0. The condenser circuits Il and Il are shown, for clarity.

- faces, or fins.

diagrammatically displaced above and to the left of the respective evaporator circuits I'I and I8. Refrigerant vapor from the compressor II (driven by power means not shown) passes through line 8 and the special three-way switching valve 20 (to be described below) and thence through line 1 to the condenser circuit I5 of the conditioning blast coil unit I3 if the conditioned air is to be warmed (Fig. 1); or through line 6 to the condenser circuit I8 of the outside air blast coil unit I4 if the conditioned air is to be cooled (Fig. 2). In each figure those sections of the complete refrigerant system which are used for the function illustrated are shown by solid lines, and those sections in which the ow is temporarily cut ofi are shown by dashed lines. Condensed refrigerant from whichever condenser is in operation enters the receiver I2 through one of the check valves 2I, the other check valve preventing any back flow through the unused condenser coil. From the receiver, liquid refrigerant is admitted during the heating cycle (Fig. 1) by the valve 22 via line 3 to the subcooling coil I 9 (see below) and via the expansion valve 24 and line 4a to the evaporator circuit I8 of outside blast coil unit I4; and during the cooling cycle (Fig. 2) by the valve 23 to the other expansion valve 24 and via line 4 to the evaporator circuit I7 of the conditioning blast coil unit I3. After evaporation in one or other of the evaporator coils, the refrigerant returns to the compressor II via lines 9.

The special switching valve 20 has been developed to facilitate electrically controlled switching of the relatively large vapor line 8 from the compressor to the condenser circuits I and I6. The valve is operated by the pressure of the vapor itself, the action being controlled as described below by the pilot valves 25 and 26 in the relatively small lines 21 and 28 leading from the two ends of the valve casing to the high pressure refrigerant line 8. The pilot valves 25 and 26 are electrically operated in unison with the valves 22 and 23 on the liquid lines leading from the receiver I2. As shown in Figs. 1 and 2, the valves 22 and 25 are always in one state and the valves 23 and 26 inthe opposite state. Operation of these four valves (the equivalent of two threeway valves) is all that is required to change the entire system from the heating to the cooling function, or the reverse.

My new system has the same simplicity of refrigerant switching as system C, described above, avoiding the relative complexity of system B. This factor has an important bearing not only `on the first cost of a plant, but also on the expense of maintenance.

The air friction in my system is much less than in system C, in which each air stream must pass through a complete idle blast coil. The presence of an additional refrigerant tube circuit in each of my blast coils increases the air friction only slightly over that in system B, since the major part of the friction occurs at the secondary sur- In my system all secondary sur-l faces of both blast coils are in full use, whether the conditioned space is being heated or cooled.

In expense, size, and weight, as in air friction, my system is decidedly superior to system C, since only half as many blast coil units are needed. Although each coil unit is somewhat more expensive than the simple coils of system B, the difference is not great. Since each tube` circuit can be designed for the single function it is to perform, the emciency of operation is adding a certain amount of fresh outdoor air from passage B to the circulated conditioned air stream in passage A in order to maintain freshness in the conditioned space. A corresponding amount of air must be expelled from the conditioned space, and provision for doing this is indicated schematically by the connecting duct 36. In general it is economical to have this exchange of air between the two main air ducts of the system take place ahead of the blast coils, since this reduces the temperature difference between the two air streams at the blast coils, and hence reduces the temperature lift of the system. However the air exchanges may take place at any suitable points in the complete system; for instance, the expulsion of air from the conditioned air circuit may be simply by air leakage from the conditioned space.

The capacity and effective efficiency of a heat transfer system of the general type under discussion' can be increased significantly by sub-cooling the condensed refrigerant before it reaches the expansion valve 24. For this purpose an auxiliary heat exchanging coil is added to the refrigerant circuit between the condenser and the expansion valve, heat being removed in this coil from the refrigerant to some other medium. On the cooling cycle any medium can be used for this purpose, provided its temperature is lower than that at which the refrigerant leaves the condenser (assuming, of course, that heat taken up by this medium does not warm the conditioned space). The same medium which is used to cool the condenser ordinarily satisfies this requirement, since a considerable temperature differential must exist between' it and the refrigerant coils of the condenser, in order to give a rapid exchange of heat.

For example, in my system when it is acting to cool the conditioned space as in Fig. 2, a refrigerant subcooling coil (not shown) might be introduced in the outside air stream in passage B ahead of the condenser I6. This would cool the liquid refrigerant nearly to the temperature of the outside air stream. The latter would be warmed slightly in the process, but not enough to raise the temperature of the condenser appreciably. If we neglect this slight change in condenser temperature (which can of course be avoided by using a. separate stream of outside air for the subcooler), the increase in cooling capacity of the system due to such a subcooler is equal to the full amount of heat which it removes from the refrigerant. Similarly, when my system is used to heat the conditioned space, as in Fig. 1, a subcooling coil can be introduced ahead of the condenser I5 in the conditioned air stream in passage A. In this case also, a given system for a given rate of power consumption is increased by the amount of heat absorbed from the subcooler by the conditioned the capacity of air stream.

The arrangement of the subcooler illustrated in Fig. 1 has marked advantages over either of the systems just described. During the heating cycle, the refrigerant subcooling coil I9 is cooled by the stream of fresh makeup air 35 before it enters the conditionedair stream. The refrigerant can be cooled in this way nearly to the temperature of the outside air stream, and yet all the heat that. is removed from it is usefully employed in heating the makeup air, and hence, effectively', in warming the conditioned space. Since the temperature change is greater than in the sbcooling arrangements described above, the resulting increase in capacity of the system is correspondingly greater. This form of subcooierpreheater is preferably used only during the heating cycle, when the demands upon the system' are ordinarily heavier than they are for cooling. Thus it tends to improve the effective balance between these two functions of the system.

As an example of the detailed design of a set of blast coil units according to my invention, Figs. 3, 3a, 3b and 3c and Figs. 4, 4a, 4b and 4c show respectively a conditioning blast coil unit and an outside air blast coil unit which have been designed to function, as described above, in a reversible cycle heating and cooling plant of 5 tons capacity. Corresponding parts of the two blast coil units are identied for clarity in these figures by the same reference numerals, except that a subscript "a is added in the case of the outside air blast coil unit. The air streams pass through both coils from bottom to top, in the aspects of Figs. 3, 3a and 4, 4a, as indicated by the arrows. Significant differences in design of the two units will be clear from the drawings. The face area (Fig. 3b) of the conditioning coil is 6 sq. it. (18" wide by 48 long), While that of the outside air coil (Fig. 4b) is 9 sq. ft. (24" wide by 54" long), allowing a larger quantity of air to be circulated efficiently through the latter.

The refrigerant condenser tube circuit in each blast coilunit is madeup of parallel tubes 55 (or 55a) joined by the distributing header 54 (or 54a) at the inlet end and by the header 55 (or 55a) at the outlet end.A These two headers are joined by the injector 53 (see Fig. 5, described below). Refrigerant vapor enters the conditioning condenser via line 1 and the outside air condenser via line 5, both leading from the switching valve 20 (Figs. 1 and 2). The condenser circuit of the conditioning coil (Fig. 3) is made up of eight horizontal rows of six tubes each; the four upper rows being connected to the upper inlet header 54, the lower four rows to the outlet header 56, and the several tubes of the'upper rows being connected in two-pass arrangement with those of the lower rows. Each of these tube passes is essentially as long as the face of the unit-48 inches. In the outside. air coil unit (Fig. 4) the condenser circuit has six horizontal rows of eight tubes each, the tubes of the three upper rows being connected in two-pass arrangement with those of the lower rows.

The evaporator tube circuits 65 are of essentially different nature, having only one row of tubes per pass, but containing many more passes. In the conditioning coil (Fig. 3) the horizontal rows are six tubes wide and make eight passes, while in the evaporator coil the rows are eight tubes wide and make six passes. The distributing headers for the evaporator circuits are shown at 64 (or 64a) on the inlet side and at 86 (or 55a) on the outlet side. Liquid refrigerant enters the conditioning and the outside air evaporators by lines 4 and 4a, respectively, and leaves as vapor by lines 9 and Sa.

In each blast coil all the tube passes of both circuits are joined by a multiplicity of parallel hns 58. These form the secondary surfaces of the unit, at which heat exchange with the air takes place. The fins shown in the figures are thicker and farther apart than they are in the actual coil. Heat conducting relationship between the fins and the tubes of the two refrigerant circuits is obtained by any of the usual methods of construction. My invention does not require that each nn contact all the tubes of both refrigerant circuits, as is the case in the particular coil units illustrated, so long as each iin or other secondary surface element is common to some part of both circuits.

The injector 53 is shown in section in Fig. 5. It consists essentially of the jet nozzle 50 lying along the axis of the tubular chamber Il, and the side tube 58 atapproximately the level of the nozzle. Refrigerant vapor enters from the high pressure line 5 or 1 at 52 and passes through the nozzle 59, creating suction through the side tube 58. As will be seen in Fig. 3 (or Fig. 4), this side tube connects to the outlet header I5 (or 58a) of the condenser. The lower part of this header contains condensed refrigerant on its way to the liquid outlet 5 (or 5a), but the upper part of the header is filled with vapor which has passed through the condenser coil circuit without being condensed. This vapor is drawn from this header by the injector and enters the inlet header 54 (or 54a) of the condenser coil circuit together with fresh vapor from the nozzle. The eiiect is to recirculate the refrigerant vapor which has not been condensed. This increases the mass flow of refrigerant through the coil, thus increasing the rate of flow and the effectiveness of heat transfer.

The increased mass flow resulting from recirculation of the uncondensed vapor also tends to wash the condensate out of condenser tubes 55 or 55a into header 56 or 55a, increasing the tube area which is in effective heat exchanging relation with the Vapor. This function of the recirculation is particularly important in condensing typical refrigerant vapors, which ordinarily have a relatively low heat of Vaporization (for example, about 60 B. t. u. per lb. for dichlorodifluoromethane, known commercially as Freon 12, compared to about 1000 B. t. u. per lb. for water), since a relatively large amount of liquid must be moved out of the condenser passages for a given amount of heat exchanged. Recirculation becomes mere eilective as the resistance to flow through the condenser passages isreduced. Such a reduction of resistance is accomplished, for example, in the illustrative embodiments described above, by the use of many condenser tubes connected in parallel, each tube making only two passes through the fins.

The discussion thus far has been limited for simplicity to the form of heat pump system in which heat is exchanged directly between the refrigerant and the conditioned air on the one hand, and directly between the refrigerant and the outside air on'the other. It is of course possible to replace the outside air stream 32 by a stream of some other medium, such as water. Each of the tube circuits of the blast coil unit I4 will then preferably be replaced by a heat exchange unit, one of which is designed to act as a condenser and the other as an evaporator. These may be supplied with fresh water, or the water may be circulated through a radiator, and heat transferred between the water and the outside air. The point of present interest is that even with such a replacement of the outside air blast coil I4, the advantages of my new type of blast coil still apply to the conditioned air stream. My invention can therefore be applied effectively under certain circumstances to the heat exchange unit in the conditioned air'stream only, or, similarly, to that in the outside air stream only. e

A preferred form of my new switching valve 2D is shown in partial section in Fig. 6. Operation of the valve depends upon the fact that vapor is delivered under pressure to the inlet port 40. and that the pressure in the lines leading from the outlet ports 4I and 4Ia (particularly in the line through which vapor flowis cut off by the valve) is maintained at a lower value by condensation of the vapor in the condensers to which these lines lead. The valve casing 39 is made in three sections, forming three concentric cylinders. The central cylinder 42 is separated from the two larger end cylinders 43 and 43a by the flat annular pieces 44 and 44a which carry valve seats 45 and 45a respectively on their inner faces. The piston 41 in the central cylinder is rigidly joined by the connecting rods 46 to the pistons 49 and 49a in the end cylinders. The central piston carries on its faces the layers of rubber-like material 48 and 48a, so that it forms a tight joint when pressed against one or other of the valve seats 45 or 45a. When piston 41 is seated against valve seat 45a, say. (as shown in Fig. 6), it cuts off communication between inlet port'40 and end cylinder 43a; but the outer face of piston 41 is still exposed to substantially the fluid pressure in end cylinder 43a. If piston 41 fits central cylinder 42 closely, the cylindrical surface of the piston acts as a sleeve valve which may supplement or replace the annular valve formations 45,

g 45a. Thus fluid entering at the centrally located inlet port 40 is diverted to one or other of the outlet ports 4I or 4Ia, located near the inner ends of the end cylinders 43 and 43a. The end pistons 49 and 49a serve to operate the valve, but take no direct part in the valving action, which is performed entirely by the central piston".

For opera-tion of the valve, the relatively small line 21 leads from a connection in the head of the left cylinder 43, through the electrically controlled pilot valve 25, to the high pressure vapor line 8 which carries refrigerant vapor from the compressor II to the inlet port 40 of the switching valve. A similar line 28 leads from the head of the right cylinder 43a through the pilot valve 26 to the line 8. A small leak, indicated schematically at 29, is provided between the head of the cylinder 43 and the outlet port 4I from this cylinder. A similar leak 30 allows a slight flow between the head of the cylinder 43a and its' outlet port 4Ia. These leaks act to bypass the pistons 49 and 49a, tending to eliminate'any pressure differential which may exist across them. Ihe leaks do not need to be located in external lines, as indicated in the figures, but can be provided, for example, by piercing the pistons themselves with one or more small apertures, or simply by allowing sufficient clearance between the pistons and the walls of the cylinders 43 and 43a.

With the pilot valve 25 open and 26 closed, the piston assembly o f the valve is normally at the right hand limit of its motion, as shown in Fig. 6, so that inlet port 40 is connected to outlet port 4I, and compressed vapor flows through line 1 to the condenser circuit I5 of conditioning unit I3, as required for the heating cycle (Fig. 1). The valve is held in this position by the dierential pressure across the central piston 41. 'Ihe left side of this piston is 'exposed to vapor entering at 40 under essentially the full pressure of the compressor. The pressure acting on the right side of this piston is that within the end cylin- `can not be higher, once equilibrium conditions are reached, than the va'por pressure of the refrigerant at the temperature of the condenser itself. The temperature of this condenser is relatively low, both because it4 is in the outside air stream and because itis in thermal contact through the fins I0 with the evaporator I8. Therefore the pressure in cylinder 43a will necessarily be lower, and ordinarily will'be much lower, than that in the central cylinder 42, and the valve will be held firmly against the seat a. Under the assumed steady state conditions, nc differential pressure acts on either one of the end cylinders 49 and 49a, due to the equalizing effects of the leaks 29 and 30.

If now the pilot valves are reversed; 25 being closed and 26 opened, vapor under pressure flows from line 8 through valve 26 and line 28 to the outer end of cylinder 43a. In spite of leakage through -30 around the piston 49a, a large pressure differential is set up, tending to move the piston assembly to the left. Since piston 39a is larger than the central piston 41, the force on it is greater than the opposite force on the central piston, and the piston assembly therefore moves to the left. As soon as contact is broken between gasket 48a on the central piston 41 and the valve seat 45a, high pressure vapor can ow from the central cylinder 42 into the right hand cylinder 43a, tending to reduce both 'the pressure differential acting on the end piston 49a and the opposite pressure differential on the central piston 41. However, this effect is small for several reasons. Vapor entering cylinder 43a ows freely out through port 4Ia and line 6 to condenser circuit I6, which was idle and cold during the previous cycle, and is there rapidly condensed.

Moreover, central piston 41 fits its cylinder well enough so that the flow around it is small. In addition, as shown in Fig. 6, this piston is preferably quite thi-ck, so that as it passes the entrance port 40 (from right to left in the present instance) it virtually cuts off the normal now through line 8. This causes a momentary surge of pressure in line 8 which is transmitted through the open pilot valve 26 and line 28 to the outer end of cylinder 43a, further accelerating the leftward motion of the piston assembly.

As the central piston approaches the left end of its cylinder, the ilow from the central to the left cylinder 43 is first sharply reduced, and then completely cut off when gasket 48 makes contact with the left valve seat 45. A pressure differential tending to'hold the Valve in this position is at once set up across the central piston.

vThis is given by the difference between virtually end of cylinder' 43a, and through outlet port 4I a f to the cold condenser circuit I6 (see above). As continued condensation of the vapor warms this 1l condenser, with corresponding increase in the vapor pressure within it, the pressure differential across piston 49a is gradually eliminated (with the help of leak 30). Therefore the valve is held in its new position by the force on the central piston only. Throughout the shift from extreme right to extreme left positions of the piston assembly, the lefil piston 49 takes no active part, the leak 29 maintaining approximate equality of .pressure throughout cylinder 43. The entire action, described here at some length, actually takes place very rapidly. The opposite motion of the piston assembly 'from' left to right is brought about in an exactly similar way when pilot valve 25 is opened and 26 is closed It will be seen that my new switching valve, operating as described above, involves no loss of refrigerant from the high to the low pressure side of the compress-or. The action takes place entirely within the high pressure part of the system between the compressor Il and the receiver I2, and' all the vapor delivered by the compressor, including that which passes through the pilot valves A25 and 26 to operate the switching valve, returns to the compressor through one or other of the condenser circuits I5 and I6. This prevents any waste of potential capacity of the system and avoids unnecessary complication in the connections.

For clarity of illustration, I have described the action of my switching valve wit-h reference to its use in a particular type of reversiblel cycle system. However, it is not limited to such use, but can be applied also to switch the flow of vapor from a supply line between any `two feed lines in which, in absence of vapor ow, the pressure is appreciably less than the pressure in the supply line. Such a reduced pressure in the feed line which is temporarily cut off from the supply line will result, for example, if vapor can escape (even at a relatively low rate) from the feed line to a region of lower pressure; or-if, as in the present instance, each feed line communicates with a check valve which prevents back flow into the line and if there is some condensatin of vapor between the switching valve and each check valve.

Fig. 7 illustrates diagrammatically an electrical control circuit of preferred form by which `the reversible cycle heating and cooling system described above can be rendered completely automatic in operation. This control system also provides automatic defrosting of the outside air blast coil unit whenever, on the heating cycle, the accumulated frost on the evaporator obstructs the passage of air to a predetermined extent. Before describing the electrical control system it-n self, it will be useful to outline the functions which this particular system is designed to perform.

Throughout those periods of the day during which temperature control is desired, the conditioned air fan 33 operates continuously, providing circulation throughout the conditioned space and drawing in a certain amount of fresh air from outside, the remainder of the system operating only if the temperature of the'reurn air from the conditioned space is colder or hotter than the desired temperature by a predetermined small diiierential x. If lthis differential is exceeded, the refrigerant control valves 22, 23, 25 and 26 are set for heating `or cooling, whichever is required, and the outside air fan 34 is started. The starting of this fan initiates the starting of the motor which drives the compressor II. 'I'his motor always starts at low speed. It changes automatically to high speed if the difference between the temperature of the return air and the desired temperature exceeds a second predetermined differential y, larger than fc. The motor then stays in high speed until it is shut off. This occurs, whether the motor is operating at high or low speed, when the air temperature comes within the differential a: of the desired value.

When the outside air temperature is low, frost may accumulate during the heating cycle on the outside air blast coil unit I4, which is necessarily colder than the outside air stream itself. Whenever the resulting obstruction to air flow through the unit exceeds a predetermined amount, the operation of deirosting is initiated. The ow of air through the blast coil unit normally causes a definite pressure differential between the air in passage B to the left and to the right of the coil unit I4 (as seen in Figs. l and 2). As frost collects on the coil, 'the resistance to air flow increases, and the pressure differential increases correspondingly. I therefore make use of a pressure sensitive device to close a switch when this pressure differential exceeds a selected value which is slightly greater than its normal value. This main defrosting control operates circuits which then automatically (l) switch the system temporarily to the cooling cycle, 2) turn off the outside air fan 34, (3) operate the compressor motor independently of the outside air fan, with which it is normally linked, and (4) start a timing device. During this mode of operation, the coil circuit I6 of the outside air unit is in use as condenser, and since the air flow over this coil is out off, essentially all the heat released in the coil by condensation of the refrigerant is available for melting the accumulated frost. After the timing device has run for a predetermined time interval, suilicient to remove the amount of frost for which the main defrosting control was set, the system is lreturned automatically to normal operation under control of the thermostat.

I turn now to the preferred embodiment of my control circuit, the essential elements of which are indicated with their electrical connections in Fig. '7. Power for the motors of the conditioning system and for the electrical control circuit is obtained from regular S-phase 220 volt alternating current lines, represented by L1, L2, and Ls, although single phase power could be used instead. The power connection for Mi, the motor which drives the conditioned air fan 33, is by the three lines 8| which lead'from Li, Le, and La, through the three normally open switches I, 2 and 3 of multiple switch relay A, to the motor M1. Thus the magnet coil of the relay A controls operation of Mi. Suitable auxiliary motor starting means and safety devices are understood to be included in this and the other motor circuits, but are omitted from Fig. 7 for clarity. Similarly, motor Mz, which drives the outside air fan 34, is connected by the three lines 82 through normally open switches I, 2 and 3 of multiple switch relay B. The compressor motor M3 is a two speed motor of any suitable type, assumed for purposes of representation to be a three phase consequent pole motor This motor is operated at low speed through the three connections 83 which lead from the power lines through the normally open switches I, 2 and 3 of controlling relay D. Power for high speed operation of M3 is brought from the power lines by the three lines 84 through normally open switches 3, 4 and 5 of relay C, switches 6 and 'I of this relay serving to connect together the three terminals of the low speed windings of the motor when it is to be operated at high speed. The energizing circuit of the magnet coil of relay D includes the normally closed switch 2 of relay C. Therefore relays C and D cannot be energized to actuate their switches at the same time, `The two relays C and D are also mechanically interlocked (by means not shown) for safety in such a way that the switches of one cannot be closed unless those of the other are open.

The motor 9| of the electric clock 19 is connected directly to L1 by the line 85 and to L2 by the lines 88 and 86, so that the clock runs contlnuously; The clock motor is linked mechanically to the switch 92 in any suitable Way, so that it will open and close the switch according to a predetermined time schedule. When the switch 92 is open the entire control system, except the clock motor itself, is disconnected from line L1, and is inoperative, the relay controlled motors M1, Mz and M3 being therefore also disconnected. When the switch 92 is closed, line 85 from L1 is connected to line 81 which leads to one side of switch 4 of relay A and also to one side of the magnet coil of this relay, the other side of which ls connected through line 86 to L2. This actuates the relay, closing all Ifour of its normallyopen switches. Switches l, 2 and 3 energize the motor M1, operating the conditioned air fan 33; and switch 4 energizes line 89 and the several short feeder lines from it, by completing 'their connections to L1. The line 90 is normally energized also, since it is connected to line 89 through the normally closed switch 4 of relay E. The lines 89 and 90, (like the line 86 and its feeder lines which are always connected to L2) are shown as heavy lines in Fig. 7. The function of the clock, then, may be expressed as energizing the line systems 89 and 90, and energizing the conditioned air fan motor M1, both being accomplished through the relay A. The green pilot light 93, connected between lines 89 and 86, indicates the functioning of this relay.

Further action of the system is thermostatically controlled in' accordance with the temperature of the return air from the conditioned space. This control is effected by means of the cam set |00, operating the switches a, b, c, d and e. .The switches a and b are mechanically linked and are operated together by the cam disk which is fixed upon shaft in a rota-tionally adjustable position. The similar camdisk |02 operates the two linked switches c and d. The actuating linger of the switch c is sufficiently wide to be contacted by either of the two separately adjustable cam disks |03 and |04. Cani shaft I|| is driven through a reduction gear, not shown, by the electric motor ||2, in such a way that it assumes a definite rotational position for every value (within a certain range) of the difference between the desired air temperature To and the actual I temperature of the return air T1. When T1 equals To the motor turns the cam shaft into the position shown in Fig. 7, in which the cam set |00 is in a. central or neutral position. As T1 drops below To, the cams are turned progressively to the left of center; and as T1 rises above To the cams are turned to the right of center, their angle of rotation increasing with the value of T1-To.

The above described temperature controlled motion of cams |00 can be obtained in many ways. I prefer to make use of an electric network and a tlvity andconvenient adjustment over a satisfacfollow-up motor, giving'great temperature sensi- 14 torily wide range of To. The essential elements of a. preferred embodiment of such a device are illustrated schematically in Fig. 7. The bulb |20, located in the return air stream 3| from the conditioned space, as indicated schematically in Figs. 41 and 2, is connected by tube |2| with the elastically extensible Sylphon bellows |22, the Whole being filled with a suitable liquid, which can be an alcohol, for example. With changing temperaupon the electrical resistance ture of the bulb, the contained liquid changes volume, expanding or contracting the bellows |22, of` which the right hand end is rigidly supported and the other end is connected to the rack |24. This moves the rack, turning pinion |25, and changing the setting of the variable contact 30 |32. Thus thefratio of the two parts into which this' resistance is divided by the contact |30 depends in a definite way upon the return air temperature T1.

A second resistance |33is similarly divided by a variable contact |3|. This contact is mounted (in principle at least) o n the same shaft ||i as 'the cam assembly |00, and is turned with it by the motor H2. One side of resistance |32 is electrically connected by line |35 to one side of resistance |33and also to line |31 leading to one side of the secondary winding of a voltage reducing transformer |40. the primary of which is connected between the lines 86 and 89. The other sides of the resistances |32 and |33 are connected together by line |35, which is also connected by line |38 to the other side of the secondary of the transformer |40. The two variable contacts |30 and |3| are connected by lines |44 and |45 to opposite sides of the armature winding ||3 of the Ielectric motor ||2. The field windings ||4 of this motor are connected by |31` and |38 across ,the secondary of transformer |40. This circuit can be considered as comprising a Wheatstones bridge, the four resistances of the bridge being formed by the four sistances |32 and 33 are divided by contacts |30 and |3|. Current is supplied to the bridge through lines |31 and |38 from the transformer |40. The armature winding of rnotor ||2 takes the place of the galvanometer usually associated with such a bridge circuit. No current will flow -in this armature if the bridge is balanced-that is,

if the resistances |32 and |33 are divided in the same ratio by their respective contacts |30 and |3|. Otherwise current will flow throughthe armature of the motor, either in phase with or in opposite phase to the current through its field windings. This will operate the motor in one direction or the other, depending upon the sense in which the bridge is out of balance. The motor Amust be so connected as to drive the contact |3| in that direction which will tend to restore the balance of the bridge circuit. Then, whenever' contact |30 is rotated by motion of its temperature 'sensitive mechanical control, the contact |3| will be similarly rotated by motor |2, carrying with it the switch actuating cam assembly |00. The cams therefore assume a definite position for each value of the return air temperature T1.

Adjustment of the temperature To for which the cams |00 will assume a central position may be accomplished in many different ways. For' purposes of illustration we may assume that the total volume available to the charge of fluid in bulb |20 and Sylphon |22 is adjustable by varying the volume of the auxiliary Sylphon |26. As this Sylphon is compressed by the screw |21, the temperature To which results in a central posi-v tion of rack |24 (and hence of cams |00) is parts into which the two re-.

lowered; and as the Sylphon |26 is expanded, this temperature is raised. An example of a complete unit which is commercially available, including thermostat, motor and cam shaft, and which performs the functions described above, is a Barber Coleman modulating control damper motor of the-D. C. 500 series.

Assuming that, by the above described means or some functional equivalent, cam set is rotated from its central position by an angle which corresponds with the difference between the desired temperature To and the existent return air temperature T1, I return now to the control circuit proper. If T1 falls below To by a certain small adjustable difference x1, the switches a and b are closed by rotation of cam |0| to the left; the value r1 depending on the adjusted normal position of the cam. Closure o! switch a connects line |60 to 90, completing circuits through four separate elements, wired in parallel, which together form what I shall call the heating set-up. These are the red pilot light ISI, the motor Ms and the two valve opening 'solenoids V1 and Va, which when energized open the Avalves 22 and 25, preparing the refrigerant circuit for the heating function, as already explained (Fig. 1). The motor Ms is not essential to the operation of my system. but can be employed to humidify the conditioned air stream, for example by pumping water through a spray nozzle. Water for this purpose can be obtained, for example, from the water which condenses from the outside air stream upon the evaporator coil |8.

The closing of switch b by cam |0| completes a circuit via line |65 through the magnet coil of .relay B from line 90 to line 86, actuating the relay and closing its four normally open switches. Three of these energize motor M2, actuating the outside air fan 34, as already explained. The fourth switch B4 energizes the magnet coil of relay D by closing the circuit from line 89 via line 66 to the central contact'e1 of double throw switch e, through its normally closed contact ez to line |61, then through normally closed relay-interlocking switch 2 of relay C to line |69 and nally through the relay magnet to line 86. The resulting actuation of relay D operates the compressor motor M3 at low speed. The system is now fully operating in its heating' function, but at low capacity.

If the return air temperature T1 continues to decrease, or if it is initially colder than Tfr-x1, the motor |2 continues to turn cam set |00 to the left. When this reaches a position corresponding .to the temperature To-y1, where y1 is some denite temperature interval larger than mi, the switch e is actuated by cam |03, the cam |0| continuing to hold switches a and b closed. Actuation of switch e disconnects e1 from ez and connects it instead to e3. 'Ihis breaks the circuit through line |61 by which relay D was energized, deactivating this relay and disconnecting thelow speed windings oi motor Ma from the power lines; and completes a circuit from the still energized line |66 Via line |68 to the magnet coil of relay C, energizing this relay in place of D.

Actuation of relay C puts the compressor motor M3 into high speed operation, as explained above.

16 the right with rising temperature and allows switch e to return to its normal position (shown in Fig. '7) relay C will remain activated, and the compressor motor will not be changed from high 'back to low speed. This avoids wear and tear and possible damage from sudden deceleration of .motor and compressor. However, operation oi motor M2 is still dependent upon continued activation of relay B. Ii this relay is deactivated (see below), switch B4 opens, breaking the circuit from line 89 through switch C1 and the magnetot relay C to line 86. This deactivates relay C, returning its switches and 2 (as well as the others) to their ynormal positions,.reestablishing the dependence of relays C and-D upon cam operated switch e.

Whether or not the system has been put into full -capacity operation by activation of switch e, it continues to operate (remaining in high speed once it reaches it) until rising temperature brings cam |0| far enough to the right to allow switches a and b to open. This occurs when the temperature difference To--T1 has decreased approximately to the value :r1 at which the switches were originally closed (see above). The opening of switch b deenergizes relay B, deactivating the outside air fan motor M2 and also breaking the circuit through switch B4 to relay C (via switch e and switch C1) or to relay D (via switch e and switch C2), depending upon whether the cam |03 did or did not operate switch e at any time during the course of that particular heating cycle.

,The opening of switch a breaks the circuit through |60 to the four elements of the heating set-up, shutting ofi the humidifying motor M5 and the red pilot light |6| and allowing the solenoid controlled valves 22 and 25 to close. Thus the entire system is returned to its original standby condition, only the conditioned air fan motor M1 continuing to operate.

When the conditioned air temperature T1 exceeds the desired temperature To by some definite It also opens switch C2, breaking the connection from switch e via lines |68 and |69 to relay D. In addition switch I of relay C closes a holding 'circuit by connecting lines |66 and |68 through differential :r2 (which need not equal the differential w1, mentioned above) cam |02 is rotated by motor ||2 far enough to the right to close switches c and d. These initiate a cooling cycle, with the compressor operating first at low capacity, much as switches a and b initiated the heating cycle described above. Switch c energizes line |62 by connecting it directly to line 89, thus energizing the four elements of the cooling set up. These are the blue pilot light |63, the motor M4, the solenoid V1 which opens valve 23, and the solenoid V4. which opens valve 26 in the refrigerant switching system. 'With these two .valves open the system is set for its cooling function (Fig. 2). Switch d connects line |65 to line 90. This energizes the magnet coil of relay B, just as was done on the heating cycle when a similar connection was made through switch b. The resulting operation of the outside air fan and the compressor takes place just as before. The motor M4 is not necessary to my system, but may be used to remove condensed water from a pan below the conditioning blast coil I2, spraying it, for example, into the outside air stream, and thus avoiding the necessity of a sewer connection from the unit. A further rise in the temperature T1 will bring cam |04 progressively around to the right until it actuates switch e, shifting the compressor motor M1 to high speed operation, just 'as described above. The motor continuesto operate at full capacity, due to the holding circuit of relay C, until cam |02, turning back to the lett with lowered air temperature, again allows 'the upper lefthand part of Fig. 7. 'I'he essential elements of this control are a pressure sensitive device by which defrosting is initiated; and a timing device, by which the defrosting operation is terminated. The other elements of the mechanism and the particular connections used are subject to wide variations within the scope of my invention.

In a preferred embodiment illustrated in Fig. 7, the pressure sensitiveunit is indicated at |8| and acts to close the normally open switch |82 when the pressure differential across the outside air blast coil exceeds a predetermined value. This action can be obtained, for example, by the construction indicated schematically in Fig. 7. The Sylphon bellows |83 and |84 are rigidly mounted at `their outer ends, and their inner movable ends are mechanically connected together and to the movable arm |86 of the switch |82. The tube |81 leads from the interior of Sylphon |83 to the outside air duct B to the left, or on the upstream side, of blast coil H (Figs. 1 and 2), where it is exposed to the static pressure in the duct. The

tube |88 similarly joins Sylphon |84 to the outside air duct on the right hand, or down-stream, side of the blast coil. ings of the positions of the tubes in Figs. 1 and 2.) The pressure differential across the blast coil, caused by the resistance it ofl'ers to the air flow, is thus transmitted to the Sylphons, causing the arm |85 to move farther to the right the greater the pressure differential. By adjusting the fixed contact of the switch, as by the thumb screw |89, the switch may be made to close at any desired value of the pressure differential. A complete unit IBI, which performs satisfactorily the functions described, is available commercially under the descriptive name "Hays contact making draft gauge, type BEL.

(See the schematic show- 'to line 86, actuating the relay. lSo long as relay E is actuated, the refrigeration system operatesI to defrost the outside air coil. Switch E1 of this relay closes the holding circuit leading from line 89 through the switch to line 203, thenthrougm the still closed switch |91 of the timer to line 202 andthence by parallel paths through the magnet coil of relay E and through the timer motor |96 to line 86. Thus the relay E and the timer, once they are activated bythe closing of pressure sensitive switch |82, remain activated through y the holding circuitl even after switch |82 opens,

as it will do early in the course of the defrosting cycle. But the opening of switch |91 by the timer, after it has run for the predetermined period, breaks this holding circuit, deactivates relay E and the timer itself, and thus returns the entire system to normal operation.

The/actuation of relay' E initiates the defrosting cycle by performing several functions. Firstly, normally closed switch E4 of the relay is opened, disconnecting .line 90 from line 89 and in eiect opening the switches a and b (which were presumably operating the system in its heating function, as already described) and also disabling switch d. This action alone would return the system to its standby condition, closing switching values 22 and 25, stopping the outside air motor Mz and compressor motor M3, but leav- Typical air flow through the particular outside air blast coil shown in Fig. 4 normally gives a pressure differential of approximately 0.4 inch of water. With a light coating of frost on the blast coil. this is increased by a few hundredths of an in-ch, and as the layer of frost becomes heavier it increases progressively. By'aiusting the unit |8| to make contact at the desired pressure differential, defrosting of the coil can lbe initiated when the frost is still light, or can be postponed until it is relatively heavy. 'I'hus any desired balance between the various factors affecting efiiciency and convenience can be obtained.

The timing device by which the defrosting operation vis terminated (see below) is also adjustable; and the duration of the defrosting operation is preferably so coordinated with the setting of the control unit |8| that just suillcient time is allowed to remove the particular depth of frost at which defrosting was initiated. The timer |95, used in the particular embodiment illustrated, is a simple commercially available device including a self-starting clock-type motor |96 and a normally closed switch |91. These are linked mechanically in such a way that the switch is opened momentarily after the motor has run for a definite adjustable period of time; and that when the electric circuit through the motor is broken, the switch is automatically reset to its closed position, ready for another cycle of operation.

When switch |82 of pressure sensitive unit |8| ing the conditioned air motor Mi in operation. Secondly, switch 3 of relay E closes the connection from line 89 via line 208 to line |68, and thence through themagnet coil of relay C to line 86. This energizes the magnet, actuatingthe relay C and putting the compressor motor Ma into full capacity operation. If the switches of relay E are so adjusted that upon actuation the relay switch E3 closes slightly before switch E4 opens, the compressor will continue uninterrupted operation, merely shifting into high speed if it was previously' in low speed. Thirdly, closure of switch Ez of the defrosting relay connects line 89 to line 209, energizing the four elements of the cooling setup, opening valves 23 and 26 of the refrigerant switching system, just as would n'ormally be done by closure of switch c. This switches the refrigerant system to its cooling function, since the valves 22 and 25 have been closed as a result of the opening of switch E4. The functional result of activation of relay E, then, is to operate the system essentially as in its normal cooling cycle, but with the outside air fan turned oil?. Therefore refrigerant coil circuit i6 is-used as condenser (Fig. 2) and heat is given up by the refrigerant to the coil. The fin structure (or its equivalent) of the blast coil forms heat conducting connection, as described above, between this coil circuit andA coil circuit i8, the use of which as evaporator during the preceding heating cycle caused the frost formation. The heat given up by one coil circuit is therefore irnmediately available for melting the frost, even though this was formed directly by cooling action of the other coil circuit. Since the outside air fan is turned ofi', this heat is not carried away to any appreciably extent by the surrounding air.

The above described automatic defrosting system avoids the waste inherent in automatic systems which initiate the defrosting cycle at reguon the blast coil. Under some weather conditions defrosting is required frequently, and if it is omitted the eiectiveness of the heating function of the system may be seriously curtailed. Under other conditions defrosting may not be required at all for many days at a time, whatever frost is formed melting ott naturally while the system is inactive or while it is cooling the conditioned space. Regular defrosting is then a waste ofv power, and interrupts unnecessarily the use of the system for heating. With my new type of defrosting control the defrosting cycle is always initiated when needed, and only `when needed. Moreover, each defrosting cycle is correctly timed for the depth of frost actually present. If it is desired to limit the initiation of defrosting cycles to certain periods of the day, this can readily be done, retaining most of the advantages of my system, by introducing a simple adjustable time switch (not shown, but similar to time switch 'I9 of Fig. 7) in series with the pressure controlled switch |82 in line 2li. When this time switch is open it will inactivate the defrosting system; when it is closed the system will operate normally, as described above. new type oi' defrosting control can be applied with little change to other kinds of dual purpose heating and cooling systems, in particular those described above as system B.

I claim:

1. In a reversible cycle heat pump of the type which includes structure embodying a conditioning passage for uid to be heated or cooled, another passage for a heat carrying fluid, means for moving a fluid to be heated or cooled through the conditioning passage, means for moving a heat carrying fluid through the other passage, a condenser coil and an evaporator coil positioned in each of the two passages in heat transferring relation to the fluid flowing therein, refrigerant conduit circuiting includingtwo parallel refrigerant circuits each of which includes the condenser i coil in one fluid passage and the evaporating coil in the other fluid passage, and valvularly controlled means for circulating refrigerant selectively through either circuit; the improvement which comprises structure forming an entrance through which a restricted amount of heat carrying fluid is introduced into the conditioning passage from the other passage, a refrigerant subr cooling coil in said entrance, and conduit means by which the sub-cooling coil is incorporated in one of therefrigerant circuits between' the condenser and the evaporator of that circuit.

2. In a reversible cycle heat'pump of the type which includes structure embodying a conditioning passage for iiuidto be heated or cooled, another passage for a heat carrying fluid, means for moving a fluid to be heated or cooled through the conditioning passage, means for movinga It will be obvious that myheat carrying fluid through the other passage,

a condenser coil and an evaporator coil positioned inv each of the two passages in heat transferring relation to the fluid flowing therein, reirigerant conduit circuiting including two parallel refrigerant circuits each ofwhich includes thecondenser coil in Vone iluld passage. and the evaporating coil in the' other iluid passage, and

valvularly controlled means for circulating refrigerant selectively through either circuit; the

-- improvement which comprises structure forming an entrance through which a restricted amount of heat carrying fluid is.introduced into the conditioning passage from the other passage, a refrigerant sub-cooling coil in said entrance, and

' 20 conduit means by which the sub-coolina coil is incorporated inthe refrigerant circuit which includes the condenser in the conditioning passage in a position in that circuit between the condenser and the evaporator inthe heat carrying passage.

3. In a reversible cycle heat pump of the type which includes structure embodying a conditioning lpassagefor fluid to be heated or cooled, another passage for a heat carrying fluid, means for moving a iluid to be heated or cooled through the conditioning passage, means for moving a heat carrying fluid through the other passage, a condenser coil and an evaporator coil positioned in each of the two passages in heat transferring relation to the fluid flowing therein, l.refrigerant conduit circuiting including two parallel refrigerant circuits each of which includes the condenser coil in one fluid passage and the evaporating coil in the other fluid passage, and valvularly controlled means for circulating refrigerant selectively through-either circuit; the improvement which comprises structure forming an entrance through which a restricted amount of heat carrying iluid is introduced into the conditioning passage from the other passage, a refrigerant sub-cooling coil in said entrance, and conduit means by which the sub-cooling coil is incorporated in the refrigerant circuit which includes the condenser in the conditioning passage in a position in that circuit between the condenser and the evaporator in the heat carrying passage, and structure forming a connecting passage through which fiuid'from the conditioning passage at a point ahead of the condenser therein is transferred in restricted amount to the heat carrying passage at a point ahead of the evaporator therein.

4. In a reversible cycle heat pump of the type which includes structure embodying a. conditioning passage for fluid to be heated or cooled, another passage for a heat carrying iluid, means for moving a fluid to be `heated or cooled through the conditioning passage, means for moving ka heat carrying fluid through the other passage, heat transfer means positioned in each of the two passages in heat transferring relation to the fluid flowing therein and adapted selectively to evaporate refrigerant liquid and to condense refrigerant vapor, and refrigerant conduit circuiting and valvularly controlled means for supplying refrigerant vapor selectively to one heat transfer means and refrigerant liquid to the other; the improvement which comprises structure forming lan entrance through which a restricted amount of heat carrying iluid is introduced into the conditioning passage from the other passage, a refrigerant sub-cooling coil in said. entrance, and conduit means by which the sub-cooling coil is incorporated in that part of the said conduit circuiting through which refrigerant liquid is supplied to the heat'exchange means in the said other passage.

5. Valvular means for selectively controlling the connection of a supply line which contains a. gaseous fluid at a normal supply pressure to either one of two feed lines, the pressure in that feed line which is not connected to the supply line being appreciably less than the supply pressure; said valvular means comprising, a valve `communication of theiniet port through the central cylinderto the actuating cylinder which communicates with that end ofthe central cylinder, pistons inthe two actuating .cylinders outwardly of the said outlet ports and connected to the piston valve to move therewith, valvularly controlled means for selectively applying ,pressure from the supply line to either of the actuating cylinders aty points outside the pistons therein, and means allowing leakage of fluid pressure from the outer end of each actuating cylinder to the outlet port of that cylinder.

6. In a reversible cycle heat pump oi' the type which includes a compressor, refrigerant cir.- cuiting including two alternatively usable refrigerant sub-circuits each including a condenser and an evaporator with an intervening ex- -pansion valve dividing each sub-sircuit into a high pressure side and a lower pressure side, circuit connection from the low Apressure side of each sub-circuit to the low pressure side of the compressor and forming, with the low pressure sides of the sub-circuits, the lower pressure side of the refrigerant circuiting, and valvular means in the high pressure side of the refrigerant circuiting for selectively connecting the high pressure side ofthe -compressor to the high pressure sides of the sub-circuits; the improvement in said valvular means which comprises. a centrai valve cylinder, two valve actuating cylinders of larger diameter than the valve cylinder and having inner ends in communication with the ends of the valve cylinder and clod at their outer ends, the central valve cylinder having a port intermediate its ends connected to the high pressure side of the compressor, outlet ports leading from the two actuating cylinders at points spaced inward of their outer ends. said outlet ports respectively connecting with the highpressure sides of the two refrigerant sub-circuits, a piston valve in the valve cylinder adapted by movement toward either end of that cylinder to close communication of the inlet port through the valve cylinder to the actuating cylinder which communicates with that end of the valve cylinder and to open communication to the other actuating cylinder, valve actuating pistons in the two actuating cylinders outward of the outlet ports and connected to the piston valve to move therewith, a leak passage eective between the opposite faces of each actuating piston, and valvularly controlled means for selectively applying pressure from one of the pressure sides of the refrigerant circuit to either' of the actuating cylinders outward of its actuating piston.

7. In a reversible cycle heat pump of the type which includes structure embodying a conditioning passage for fluid to be heated or cooled, another passage for a heat carrying fluid, means for moving a fluid to be heated'or cooled through the conditioning e. means for moving a heat carrying fluid through the otherpassage, a condenser coil and an evaporator coil positioned in each of the two passages in heat transferring relation to the fluid flowing therein, a refrigerant compressor, a pair of parallel refrigerant circuit conduits each leading from the oompression side of -the compressor through the condenser in one of the fluid passages andthenc'e A22 through theevaporator in the other fluid passage and thence back to the inlet side of the compressor; the improvement in valvular means for selectively controlling the connection of the compressor to the ytwo parallel circuits which comprises, a valve casing forming a central valve cylinder with annular valve seats at each end and two valve actuating cylinders extending from the ends oi the centralvalve cylinder and of larger diameter than the latter. a piston valve in the central valve cylinder, pistons in thevtwo actuating cylinders connected to the piston valve to move therewith, an inlet port connected vto the compression side of the refrigerant compressor and leading into the central -valve cylinder medially between its ends, outlet ports leading from the two actuating cylinders at points inward of the pistons therein, said outlet ports each connecting to one of the two parallel refrigerant circuits, and valvularly controlled means for selectively applying pressure from the compression side of the refrigerant compressor to each of the actuating cylinders at their outer ends outside of the pistons therein.

conduits each leading from' the compression side of the compressor through the condenser in one of the fluid passages and thence through the evaporator in the other fluid passage and thence .provement in valvular means for selectively controlling the connection of the compressor to the two parallel circuits which comprises, a valve casing forming a central valve cylinder with annular 46 valve seats at each end and two valve actuating cylinders yextending from the ends of the central valve cylinder and of larger diameter than the latter, a piston valve in the central valve cylinder,

pistons in the two actuating cylinders connected to the piston valve to move therewith, an inlet port connected to the compression side of the refrigerant compressor and leading into the central valve cylinder medially between its ends, outlet ports leading from the two actuating cylinders at 55 points inward of the pistons therein, said ports` each connecting to one of the two parallel refrigv erant circuits, valvularly controlled means for selectively applying pressure from the compression side of the refrigerant compressor to each of 00 the actuating cylinders at their outer ends crutside of the pistons therein. and means allowingY leakage of pressure fluid from the outer end of each actuating cylinder to the outlet port of that cylinder.

9. In a reversible cycle heat pump of the type which includes structure embodying a condition'- ing passage for fluid to be heated or cooled. another passage for a heat carrying fluid. means for moving a fluid to be heated or cooled through the conditioning passage. means for moving a heat carrying fluid through the other passage,

a condenser coil and an evaporator coil positioned in each of the two passages in heat transferring relation to the fluid flowing therein, refrigerant conduit circuiting including two paral- 8. In a reversible cycle heat pump of the typek back to the inlet side of the compressor; the ilne lel refrigerant circuits each of which includes the condenser coil in one iluid passage and the evaporating coil in the other fluid passage, and valvularly controlled means for circulating refrigerant selectively .through either circuit; the improvement which comprises, an element responsive t'o changes of the fluid pressure differential between opposite sides of the evaporator in the passage for the heat carrying fluid, and means controlled by said element, upon said pressure differential exceeding a predetermined value, to actuate the valvularly controlled means to circulate' refrigerant through that refrigerant circuit which includes the condenser in said fluid passage.

10. Improvements in reversible cycle heat pumps as defined in claim 9, and in which the means controlled by the pressure responsive element includes a timing device acting to control valvular means remains in its said actuated condition.

the time period during which the valvular means remains in its saidactuatedcondition.

1l. Improvements in reversible cycle heat pumps as defined in claim 9, and in which the means controlled by the pressure responsive element includes a timing device acting to limit the time period during which the valvular means remains in its said actuated condition, and in which said means also includes means acting to de-activate the fluid moving. means of the heat carrying passage for the duration of said time period.

12. In a refrigerating system which includes a heat transfer element of the blast coil type, means for circulating refrigerant therethrough and means for moving a vapor containing gas through the heat transfer element, whereby the gas is cooled and some of its contained vapor deposited inl solid form on the element; the improvement which comprises the combination of means for-supplying heat to the transfer elei-ment, and a controlsystem for said heat supplying means, said control system including a control element responsive to changes in the gas pressure differential at opposite sides of the heat transfer element.

13. The improvement defined in claim 12 and in which the control system also includes means by which the initiation of heat supply is effected by said control element, and timing means controlling the termination of heat supply.

14. In a reversible cycle heat pump of the type embodying a passage for a heat carrying gas which may contain a vapor, means for moving such gas through the gas passage, an evaporation coil of the blast type in the gas passage in heat transferring relation to the gas flowing therein, and refrigerantI circuiting including ,valvularly controlled means for supplying either a refrigerant or heat to the evaporator; the improvement/which comprises, an element responsive to changesvin the gas pressure differential between opposite sides of the-evaporatorin the gas passage, and means controlled by said ele- 'ment, upon said pressure differential exceeding a predetermined value, to actuate the valvularly controlled means to supply heat to the evaporator.

15. The improvement deilned in claim 14 and also including a time controlled element acting to control the time period during which the 16. In a reversible cycle heat pump of the type embodying a passage for a heat carrying gas 'which may contain a vapor, means for moving such gas through the passage, evaporator and condenser coils 4of the blast type in the gas passagein heat transferring relation to the gas flowing therein, refrigerant circuiting including 4valvularly controlled means for selectively supplying either condensed refrigerant to the evaporator or hot compressed refriger-ant vapor to theV condenser; the improvement which comprises the combination of a heat transfer unit which includes the evaporator and condenser coils and heat transfer elements common to both coils and affording a heat transfer path between the coils, and a defrosting system comprising control means responsive to thevdeposition of frost on the evaporator and acting to actuate thevalvularly controlled means to supply hot compressed refrigerant vapor to the condenser coil of the heat transfer unit.

17. The improvement defined-in claim 16 and also including a time controlled element acting tov control the time .period during which the valvular means remains in its said actuated condition.

18. A condenser embodying structure forming a passage for condensible vapor and condensate and heat transfer surfaces associated with the passage, an inlet passage leading to one end of the condenser passage, an outlet passage leading from the other end of the condenser passage, means associated with the inlet pasi sage and acting to create in said passage a localcirculated through the condenser passage.

19. A condenser as defined in claim 18 and in which the condenser structure includes a plurality of heat conductive ilns, in which the condenser passage is formed by a plurality of tubes each of which makes two passes through the fins, and including an inlet header forming a part of the inlet passage to the tubes, an outlet header forming a part of the outlet passage leading from the tubes, and in which the location of lowered pressure in the inlet passage is substantially on a level with the upper part of the outlet header and. the communication with theoutlet passage is .directly with the outlet header.

GILBERT E. CLANCY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES vPATENTS 

